Due to its characteristics of being easily applicable to various products and electrical characteristics such as a high energy density, a secondary battery is not only commonly applied to a portable device, but universally applied to an electric vehicle (EV), a hybrid vehicle (HV), or an energy storage system that is propelled by an electric motor. This secondary battery is gaining attention for its primary advantage of remarkably reducing the use of fossil fuels and not generating by-products from the use of energy, making it a new eco-friendly and energy efficient source of energy.
A battery pack for use in electric vehicles has a structure consisting of a plurality of battery assemblies connected in series, each battery assembly including a plurality of unit cells, to obtain high voltage. Also, the unit cell includes a cathode current collector and an anode current collector, a separator, an active material, and an electrolyte solution, and allows repeated charging and discharging by electrochemical reactions between the components.
In addition to this basic structure, the battery pack further includes a battery management unit (BMU) to monitor and control a state of a secondary battery by applying an algorithm for control of power supply to a driving load such as a motor, measurement of electrical characteristic values such as current or voltage, charge/discharge control, voltage equalization control, state of charge (SOC) estimation, and the like.
Recently, with the increasing need for a high-capacity structure as well as utilization as an energy storage source, the demand for a battery pack of a multi-module structure in which a plurality of battery modules including a plurality of batteries connected in series and/or in parallel are assembled, is also increasing.
Because the battery pack of the multi-module structure includes a plurality of batteries, there is a limitation in controlling the charge/discharge state of all the batteries using a single BMU. More recently, technology that mounts a BMU in each battery module included in the battery pack to build a battery management system (BMS) is being used.
Because the battery pack of the multi-module structure generally has a high operating voltage, an external device connected to the BMS needs to be electrically separated.
In relation to this, Korean Patent Laid-open Publication No. 10-2011-0027189 discloses a method for electrically separating an external device connected to a BMS.
FIG. 1 is a circuit diagram illustrating a method for disconnecting an external device from a BMS according to a related art.
Referring to FIG. 1, by connecting a plurality of opto-couplers 1-#1˜1-#N to signal output terminals of a battery pack P, the battery pack P may be electrically separated from an external device Ex while respectively transmitting information to the external device Ex. According to the related art, to transfer information between the BMS of the battery pack and the external device, a large amount of opto-couplers are needed. In other words, a number of opto-couplers required increases in proportion to a number of output terminals of the BMS. However, because an opto-coupler is an electrical element more expensive than a general electrical element, it is not economically efficient to provide one opto-coupler to each output terminal.
Therefore, there is a need for a method for disconnecting a BMS from an external device with a reduced production cost of the BMS.